# Gitian

Read about the project goals at the [project home page](https://gitian.org/).

This package can do a deterministic build of a package inside a VM.

## Deterministic build inside a VM

This performs a build inside a VM, with deterministic inputs and outputs.  If the build script takes care of all sources of non-determinism (mostly caused by timestamps), the result will always be the same.  This allows multiple independent verifiers to sign a binary with the assurance that it really came from the source they reviewed.

## Prerequisites:

### Gentoo:

    layman -a luke-jr  # needed for vmbuilder
    sudo emerge dev-vcs/git net-misc/apt-cacher-ng app-emulation/vmbuilder dev-lang/ruby
    sudo emerge app-emulation/qemu
    export KVM=qemu-system-x86_64

### Ubuntu:

This pulls in all pre-requisites for KVM building on Ubuntu:

    sudo apt-get install git apache2 apt-cacher-ng python-vm-builder ruby qemu-utils

If you'd like to use LXC mode instead, install it as follows:

    sudo apt-get install lxc

### Debian:

See Ubuntu, and also run the following on Debian Jessie or newer:

    sudo apt-get install ubuntu-archive-keyring

On Debian Wheezy you run the same command, but you must first add backports to your system, because the package is only available in wheezy-backports.

### OSX with MacPorts:

    sudo port install ruby coreutils
    export PATH=$PATH:/opt/local/libexec/gnubin  # Needed for sha256sum
    
### OSX with Homebrew:

    brew install ruby coreutils
    export PATH=$PATH:/opt/local/libexec/gnubin    

#### VirtualBox:

Install virtualbox from http://www.virtualbox.org, and make sure `VBoxManage` is in your `$PATH`.

## Create the base VM for use in further builds
**NOTE:** requires `sudo`, please review the script

### KVM

    bin/make-base-vm
    bin/make-base-vm --arch i386

### LXC

    bin/make-base-vm --lxc
    bin/make-base-vm --lxc --arch i386

Set the `USE_LXC` environment variable to use `LXC` instead of `KVM`:

    export USE_LXC=1

### VirtualBox

Command-line `VBoxManage` must be in your `$PATH`.

#### Setup:

`make-base-vm` cannot yet make VirtualBox virtual machines ( _patches welcome_, it should be possible to use `VBoxManage`, boot-from-network Linux images and PXE booting to do it). So you must either get or manually create VirtualBox machines that:

1. Are named `Gitian-<suite>-<arch>` -- e.g. Gitian-lucid-i386 for a 32-bit, Ubuntu 10 machine.
2. Have a booted-up snapshot named `Gitian-Clean` .  The build script resets the VM to that snapshot to get reproducible builds.
3. Has the VM's NAT networking setup to forward port `localhost:2223` on the host machine to port `22` of the VM; e.g.:

```
    VBoxManage modifyvm Gitian-lucid-i386 --natpf1 "guestssh,tcp,,2223,,22"
```

The final setup needed is to create an `ssh` key that will be used to login to the virtual machine:

    ssh-keygen -t dsa -f var/id_dsa -N ""
    ssh -p 2223 ubuntu@localhost 'mkdir -p .ssh && chmod 700 .ssh && cat >> .ssh/authorized_keys' < var/id_dsa.pub

Then log into the vm and copy the `ssh` keys to root's `authorized_keys` file.

    ssh -p 2223 ubuntu@localhost
    # Now in the vm
    sudo bash
    mkdir -p .ssh && chmod 700 .ssh && cat ~ubuntu/.ssh/authorized_keys >> .ssh/authorized_keys

Set the `USE_VBOX` environment variable to use `VBOX` instead of `KVM`:

    export USE_VBOX=1

## Sanity-testing

If you have everything set-up properly, you should be able to:

    PATH=$PATH:$(pwd)/libexec
    make-clean-vm --suite lucid --arch i386

    # For LXC:
    LXC_ARCH=i386 LXC_SUITE=lucid on-target ls -la

    # For KVM:
    start-target 32 lucid-i386 &
    # wait a few seconds for VM to start
    on-target ls -la
    stop-target

## Building

Copy any additional build inputs into a directory named _inputs_.

Then execute the build using a `YAML` description file (can be run as non-root):

    export USE_LXC=1 # LXC only
    bin/gbuild <package>.yml

or if you need to specify a commit for one of the git remotes:

    bin/gbuild --commit <dir>=<hash> <package>.yml

The resulting report will appear in `result/<package>-res.yml`

To sign the result, perform:

    bin/gsign --signer <signer> --release <release-name> <package>.yml

Where `<signer>` is your signing PGP key ID and `<release-name>` is the name for the current release.  This will put the result and signature in the `sigs/<package>/<release-name>`.  The `sigs/<package>` directory can be managed through git to coordinate multiple signers.

After you've merged everybody's signatures, verify them:

    bin/gverify --release <release-name> <package>.yml


## Poking around

* Log files are captured to the _var_ directory
* You can run the utilities in libexec by running `PATH="libexec:$PATH"`
* To start the target VM run `start-target 32 lucid-i386` or `start-target 64 lucid-amd64`
* To ssh into the target run `on-target` or `on-target -u root`
* On the target, the _build_ directory contains the code as it is compiled and _install_ contains intermediate libraries
* By convention, the script in `<package>.yml` starts with any environment setup you would need to manually compile things on the target

TODO:
- disable sudo in target, just in case of a hypervisor exploit
- tar and other archive timestamp setter

## LXC tips

`bin/gbuild` runs `lxc-execute` or `lxc-start`, which may require root.  If you are in the admin group, you can add the following sudoers line to prevent asking for the password every time:

    %admin ALL=NOPASSWD: /usr/bin/lxc-execute
    %admin ALL=NOPASSWD: /usr/bin/lxc-start

Right now `lxc-start` is the default, but you can force `lxc-execute` (useful for Ubuntu 14.04) with:

    export LXC_EXECUTE=lxc-execute

Recent distributions allow lxc-execute / lxc-start to be run by non-priviledged users, so you might be able to rip-out the `sudo` calls in `libexec/*`.

If you have a runaway `lxc-start` command, just use `kill -9` on it.

The machine configuration requires access to br0 and assumes that the host address is `10.0.2.2`:

    sudo brctl addbr br0
    sudo ifconfig br0 10.0.2.2/24 up

## Tests

Not very extensive, currently.

`python -m unittest discover test`